interseting propulsion system

[colinwcolclough]

Has anyone come across the jet pac from the usa before? Have a look at the website www.jetpac.us Any thoughts?

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[ongolo]

Knowing nothing other than what the site says and knowing a little about boats and engines, I would say:

It has low bollard pull and is suitable only for high speed craft. a 150 Hp motor must weigh about 400kg with all accessories and a 375Hp engine maybe 550 or 600kg.

Then the cooling would be probably be raw water which is not good for an automotive engine.

For a heavy displacement boat not suitable and a light displacement boat with that thing hanging at the stern it would not be a light displacement boat any longer.

I would not touch it with a stick, besides it is made in USA.

Ongolo

<hr width=100% size=1>So what......... it floats

 

[bob26]

Its freshwater cooled in fact and rather than hanging on the back (like an outboard) seems to sit in the water in its own extension to the hull. Might therefore improve dispalcement speed because of longer watreline length and pixs on the website suggest plaing is more than feasible. Its not very elegant to my eye but then neither are wopping great outboards. Jetdrive is much safer for watersports like skiing and for club rescue boats etc as there is no bare prop to chew people up but its not for sailing types like me - though I'd give the 275hp V8 Chevvy version a go on my Mirror just to see what it can do if they are looking for a UK test boat...

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[alahol2]

I think you've got the wrong idea. It's a new type of sea toilet, cleverly combining a macerator with direct overboard ejection of the waste. I suspect, in this country, we'd expect a bit more privacy so I could see the return of the poop deck doghouse.

<hr width=100% size=1><A target="_blank" HREF=http://www.troppo.co.uk> Follow the Tightwad Sailor</A>

 

[cliff]

Quote" the whole power train is outboard" according to the web site.

I don't fancy the idea of shoving a bloody big V8 on the back of a boat bot designed for it..

If you want a jet boat why not buy a proper power unit?.

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[wooslehunter]

Wouln't necessarily go for this one (automotive etc.) but jet drives have many advantages over props. Generally as above they're used for high speed boats.

Advantages:
No prop to mangle swimmers.
No prop to get rope wound around - there's generally a grid over the intake which can be raked if something covers it.
Very shallow draft.
Very manuouvreable - can steeer with no forward motion. For neutral 1/2 of the water is directed forward by a scoop (called the bucket) dropped over the jet flow. You can have power on for steering with no net forward thrust.
No gearbox to shift to get reverse so can actually crash stop in emergencies although not recommended - just move the bucket down.
Single Castoldi jet + 330hp inboard = 0.75 ton bollard pull - how much do you want?

Disadvantages:
No fin below the water line so boats tend to wander at low speed.
Cavitation when the boat flies.
Need to keep the impellor in good nick - performance degrades faster than a prop if it's nicked by stones etc. - what are you doing in shallow water anyway.
Not so many choices.

Any other ideas?

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[cliff]

I agree with what you say but my question was "if you want a jet boat, why not buy a proper power unit" perhaps I should have added like the mercury units or the Evinrudes etc which are inboard units sucking the water through the hull and spitting it out the stern rather than sticking one of the other on the back of the transom like an outboard.

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